Earthmoving machines, for example excavating equipment, are commonly used to move large amounts of earth, rocks or other work materials. Excavators, including backhoes and other types of excavating equipment, include a boom member extending from and pivotally connected to a main body of the machine. Further, a stick member is pivotally connected to the boom member opposite the connection to the main body, and an implement, often a bucket, is pivotally attached to a nose end of the stick member. While these types of excavators are well suited for moving loose dirt and small rocks, the buckets are not as well suited for picking up larger objects that do not fit easily into the bucket. Excavators may be fitted with an additional attachment, such as a fixed or movable thumb, that opposes the movement of the implement and facilitates grabbing and moving rocks, pipes, concrete, trees, and other larger awkward objects.
The movable thumbs are manipulated by an actuation mechanism such as a hydraulic cylinder and accompanying control valve. The cylinder of the mechanism is connected between the thumb and a bracket provided on the stick member. The cylinder may have an end connected to the thumb directly (no-link type thumb), or may be connected indirectly by a linkage (link-type thumb) for greater range of thumb rotation. In previously known machines, the stick member typically requires different bracket locations for a link-type thumb and a no-link type thumb. Dealers or operators may need to weld brackets on the stick member at the work location separately for the link-type thumb and the no-link type thumb since each type requires the bracket to be placed in a different location. Configuring machines with brackets for both link-type and no-link type thumbs is not economically practical. On-location welding of the brackets to the stick member may reduce the life of the stick member which has been post-weld stress-relieved at the machine factory. To overcome the problem set forth above, one solution is to modify the design of the no-link cylinder to allow for a consistent bracket location on the stick member for the link-type thumb and the no-link type thumb. U.S. Pat. No. 5,167,182 to Sims discloses a fluid actuator assembly comprising a plurality of modules that are secured in serial relation to form a body of the fluid actuator such that the length of the actuator may be varied. However, the reference does not suggest implementation of the fluid actuator assembly to drive a movable thumb.
In addition to cylinder length considerations, adaptation of the stick member to accommodate both link-type and no-link type thumbs with a single mounting bracket position creates issues with ensuring that both thumb types perform adequately in cooperation with the implement. Both thumb types must have the thumb rotation required to grasp work material that will be moved by the machine, and must impart sufficient force to engage and retain the work material. At the same time, the thumbs must be capable of retracting to a stowed position where the thumbs will not interfere in the operation of the implement when the thumbs are not in use. For these reasons, a need exists for implement assemblies having a single point of attachment for both link-type and no-link type thumb assemblies as well as for criteria for designing and evaluating designs of thumb and stick member arrangements that will provide acceptable performance with both link-type and no-link type thumb assemblies.